Due to crusade many regions of Semigallia and Courland were left depopulated so already during the war and also after it part of the Latgalians migrated to those regions. Subsequently between 13th and 16th centuries, they gradually assimilated other Baltic tribes Selonians, Semigallians and Curonians who thus became a part of today's ethnic Latvians.

In the lands of the Western and the Eastern Latgalians, about 80 flat cemeteries of Western Latgalian origin have been excavated, with more than 2,000 burials uncovered. The first large scale excavations took place in Ludza Odukalns Cemetery in Latgale (1890–1891), where 339 Late Iron Age burials were uncovered. In the excavations at Pildas Nukši Cemetery (in Latgale, 1947–1948), 218 burials were uncovered, dated to the 9th–12th century.

At the Zvirgzdenes Kivti Cemetery (in Latgale: 1948, 1955–1958) 175 burials from the 7th–12th century were excavated. 315 burials were found at Aglonas Kristapiņi Cemetery (in Latgale; 1928, 1938, 1977–1980, 1984–1987, 1999–2000), in use from the late 8th to 12th century.

Ērgļu Jaunāķēni Cemetery was totally excavated in 1971–1972, with 89 burials being found. At Koknese Cemetery 102 burials from the Late Iron Age were uncovered (1986–1989). In the area of Gauja's Latgallians two cemeteries, Drabešu Liepiņas and Priekuļu Ģūģeri are well excavated too.

Archaeological excavations have also been carried out on the hillforts of Ķente, Koknese, Sārumkalns, Tanīskalns, as well as on other Latgalian sites. Only a few (Western) Latgalian settlements have been excavated. Large scale excavations (1960s–1970s) and reconstruction has been done at the Āraiši lake dwelling site (9th century).

In Latgale, dating from the 6th–7th centuries, there were flat cemeteries as well as barrow cemeteries. In the 9th–10th century the transition started from flat graves to barrows. There are about 15 excavated Eastern Latgalian barrow cemeteries, but usually only a small number of barrows were investigated.

Archaeologically identified dwelling-sites in Latgale include hill forts, settlements and lake dwellings. Among hillforts, well researched is Jersika Hillfort (excavated in 1939 and from 1990 onwards), forming complex together with Dignāja Hillfort, on the opposite bank of Daugava. Jersika was occupied in the 10th–14th century, probably after the decline of Dignāja, which had been inhabited since the 6th century.

It is possible that ancestors of the so-called Eastern Latgalians migrated to the territory of present-day Latgale in the 7th and 10th–11th centuries, pushed from their previously inhabited territory by Slavic migration; some archaeologists also believe that the Eastern Latgalians formed from the most ancient East-Baltic inhabitants of Latvia, who lived in central and Eastern parts of Latvia in the "Roman" Iron age (1st–4th centuries).